The invention relates to an excavator and conveyor for an underground jacking apparatus for pipelines having a preferably non-man-sized rated cross section, which is driven into the surrounding soil from a manhole and comprises a digging head and at least one follower; means being provided for jacking the digging head, and introducing other jacked lengths of pipe as soil is removed. Rotating in the end area of the digging head is a digging disc which is set into rotation by a shaft. The shaft is surrounded at a distance by a conveyor tube, the wall of which is compartmentalized with respect to its outer cylindrical jacket in the vicinity of the digging head. Conveyor means are provided in the conveyor tube for conveying the excavated material back to the manhole. Sluice means are also provided in the conveyor cross section between the shaft and the conveyor tube wall, which serve to prevent incursions of groundwater.
A sluice means of this kind is known from German Offenlegungsschrift DE-OS No. 32 28 684. The sluice means comprises a diaphragm, firmly fastened at its periphery to the conveyor tube wall, by means of which compartmentalization to prevent groundwater incursions is to be attained. The service life of such a diaphragm is limited, however. The diaphragm is used in a conveyor that is part of an apparatus for jacking product pipes or lengths of product pipe, the pipes having non-man-sized rated cross sections. The jacking of the pipelines is done with the aid of the jacking apparatus, from a manhole sunk into the soil. From the manhole, a shaft is extended outward through the conveyor tube as far as a digging head; this shaft turns a digging disc inside the digging head for the removal of soil from the area. The excavated soil is conveyed backward to the manhole by the conveyor screw surrounding the shaft. From the manhole, the soil is carried to the surface and removed from the site. To prevent the excavated soil from getting in between an outer cylindrical jacket of the digging head and the following jacked product tubes, on the one hand, and between this jacket and the smaller-diameter conveyor tube, on the other, the outer cylindrical jacket of the digging head is compartmentalized with respect to the conveyor tube by means of a frustoconical driving shield.
When the existing soil contains a varying amount of groundwater from one time to another, then its flowability varies as well. Until now, compartmentalization was done by making it substantially completely watertight, either by means of the diaphragm according to German Offenlegungsschrift 32 28 684, or by means of a plain plug of material or soil as described in German Patent No. 35 13 578.